Abstract

Diode-laser second-derivative modulation spectrometry is a simple means of measuring trace concentrations of small molecules in the gas phase. For a setup with a reference cell used both for laser frequency locking and as a concentration standard, the calibration algorithm is developed for the general case of nonvanishing nonlinear terms in the power expansion of Beer’s law in both the sample and reference channel. A practical example is given.

© 1984 Optical Society of America

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References

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  1. P. Pokrowsky, W. Herrmann, SPIE Technical Meeting on Optics and Electro Optics, 20–24, Apr. 1981, Washington, D.C., GKSS 81/E/23 (1981).
  2. P. Pokrowsky, Thesis, Universität Hamburg, Germany, 1981; GKSS 81/E/34 (1981).
  3. U. Lenhard, R. N. Schindler, IAMAP Third Scientific Assembly, 17–28 Aug. 1981, Hamburg, Germany, “IAMAP at Hamburg 1981/ICACGP” (1981), p. 89.
  4. C. Weitkamp, Third International Ocean Disposal Symposium, 12–16 Oct. 1981, Woods Hole, Mass., GKSS 81/E/57 (1981).
  5. C. Weitkamp et al., GKSS 83/E/10 (1983).

1983

C. Weitkamp et al., GKSS 83/E/10 (1983).

Herrmann, W.

P. Pokrowsky, W. Herrmann, SPIE Technical Meeting on Optics and Electro Optics, 20–24, Apr. 1981, Washington, D.C., GKSS 81/E/23 (1981).

Lenhard, U.

U. Lenhard, R. N. Schindler, IAMAP Third Scientific Assembly, 17–28 Aug. 1981, Hamburg, Germany, “IAMAP at Hamburg 1981/ICACGP” (1981), p. 89.

Pokrowsky, P.

P. Pokrowsky, W. Herrmann, SPIE Technical Meeting on Optics and Electro Optics, 20–24, Apr. 1981, Washington, D.C., GKSS 81/E/23 (1981).

P. Pokrowsky, Thesis, Universität Hamburg, Germany, 1981; GKSS 81/E/34 (1981).

Schindler, R. N.

U. Lenhard, R. N. Schindler, IAMAP Third Scientific Assembly, 17–28 Aug. 1981, Hamburg, Germany, “IAMAP at Hamburg 1981/ICACGP” (1981), p. 89.

Weitkamp, C.

C. Weitkamp et al., GKSS 83/E/10 (1983).

C. Weitkamp, Third International Ocean Disposal Symposium, 12–16 Oct. 1981, Woods Hole, Mass., GKSS 81/E/57 (1981).

GKSS 83/E/10

C. Weitkamp et al., GKSS 83/E/10 (1983).

Other

P. Pokrowsky, W. Herrmann, SPIE Technical Meeting on Optics and Electro Optics, 20–24, Apr. 1981, Washington, D.C., GKSS 81/E/23 (1981).

P. Pokrowsky, Thesis, Universität Hamburg, Germany, 1981; GKSS 81/E/34 (1981).

U. Lenhard, R. N. Schindler, IAMAP Third Scientific Assembly, 17–28 Aug. 1981, Hamburg, Germany, “IAMAP at Hamburg 1981/ICACGP” (1981), p. 89.

C. Weitkamp, Third International Ocean Disposal Symposium, 12–16 Oct. 1981, Woods Hole, Mass., GKSS 81/E/57 (1981).

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Figures (4)

Fig. 1
Fig. 1

Experimental arrangement.

Fig. 2
Fig. 2

Schematic representation of the detector power vs frequency in the signal (a and c) and reference channel (b and d) without (b) and with partially saturated absorption (d). The signal from the unknown sample (a and c) will not strongly saturate in most practical conditions, but deviations from linearity may have to be taken into account if a large dynamic concentration range is required.

Fig. 3
Fig. 3

Section through the calibration surface (calibration curve) for the following values of parameters: laser mode output power as measured by White cell and reference detectors (UW,UR) 2900, 55 mV; reference absorption peak depth (PR) 40 mV; effective cell lengths (lW,lR) 60, 0.06 m; reference gas concentration (cR) 0.01; reference channel 2f lock-in signal (SR) 1 mV.

Fig. 4
Fig. 4

Concentration of HCl 20-m above sea level in the plume of incineration ship M/T Matthias II on 24 June 1982. The course of the R/V Tabasis is also indicated.

Tables (1)

Tables Icon

Table I Comparison of Wet Chemical and Diode-Laser Determination of HCl Concentrations

Equations (13)

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I = I 0 exp [ - n l σ ( ν ) ] ,
d n d ν n I I 0
d 2 d ν 2 ( I I 0 ) = n l [ n l ( d σ d ν ) 2 - d 2 σ d ν 2 ] exp ( - n l σ ) .
σ = σ 0 exp { - [ ( ν - ν 0 ) / w 2 ] 2 } ,
d 2 d ν 2 ( I I 0 ) | ν 0 = 8 n l σ 0 w 2 exp ( - n l σ 0 ) .
y n l σ 0 = c l Σ 0 ,
d 2 I d ν 2 | ν 0 = ( 8 I 0 / w 2 ) y exp ( - y ) ,
S W = ɛ W d 2 I W d ν 2 | ν 0 ,             S R = ɛ R d 2 I R d ν 2 | ν 0
U W , U R , P R
P R = U R [ 1 - exp ( - c R l R Σ 0 ) ] ,
Σ 0 = 1 c R l R ln U R U R - P R .
S W = U W · 8 w 2 c W l W Σ 0 exp ( - c W l W Σ 0 ) , S R = U R · 8 w 2 c R l R Σ 0 exp ( - c R l R Σ 0 )
z ( S W , S R , U W , U R , P R , l W , l R , c R ; c W ) exp ( - Σ 0 l W c W ) - c W 1 c R S R U W l W S W U R l R exp ( - Σ 0 l R c R ) = 0 ,

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